Water load

ABSTRACT

A radio frequency water load is disclosed having a loss section of transmission line. The loss section of transmission line includes a delay line portion for slowing the group velocity of wave energy traveling in the loss section. Conduits are arranged for directing a stream of wave-attenuative liquid through the loss section in wave-energy-exchanging relation with wave energy on the delay line for attenuating the wave energy, whereby the physical length of the loss section is reduced for a given amount of attenuation. In a preferred embodiment, the loss section is a section of coaxial line and the inner conductor is a helical delay line.

United States Patent 3,121,204 2/1964 Giordano: 333122 FOREIGN PATENTS598,198 2/1948 GreatBritain....' 333/22 815,501 10/1951 Germany 333/22Primary Examiner-Herman Karl Saalbach Assistant ExaminerMarvin NussbaumAttomeyStanley Z. Cole ABSTRACT: A radio frequency water load isdisclosed having a loss section of transmission line. The loss sectionof transmission line includes a delay line portion for slowing the groupvelocity of wave energy traveling in the loss section. Conduits arearranged for directing a stream of wave-attenuative liquid through theloss section in wave-energy-exchanging relation with wave energy on thedelay line for attenuating the wave energy, whereby the physical lengthof the loss section is reduced for a given amount of attenuation. In apreferred embodiment, the loss section is a section of coaxial line andthe inner conductor is a helical delay line.

WATER WATER LOAD DESCRIPTION OF THE PRIOR ART I-Ieretofore, coaxialwater loads have been'constructed wherein a conically shaped teflonpartitioning wall was provided interconnecting the inner and outerconductors of the coaxial load to form a transition from air-filledcoaxial line to I waterfilled coaxial line, such water-filled section ofcoaxial line providing dielectric loss in the water.

One of the problems with this prior art coaxial water load was thattheteflon was relatively difficult to seal and to machine. In addition, thecoaxial load'was excessively long due to the long taper for the coneneeded to get the wave energy into thewater'without reflection and toaccommodate the long path length in water to absorb the energy. It wouldbe desirable to provide an improved length and employing a disc-shapedwater barrier to prevent having to seal and machine the teflon cone.

SUMMARY OF-THE PRESENT INVENTION The principal object of the presentinvention is the provision of an improved water load.

One feature of the present invention is the provision of a water loadhaving a loss section of transmission line including a delay lineportion for slowing'the group velocity of the wave energy to beattenuated and including means for directing a stream of wave energyattenuative liquid through the loss section in wave-energy-exchangingrelation with the wave energy on the delay line.

Another feature of the present invention is the same as the precedingfeature wherein the loss section of transmission line is a section ofcoaxial line and'the delay line portion of the transmission line isformed by the inner conductor.

Another feature of the present invention is the same as the immediatelypreceding feature wherein the delay line inner conductor is a helix ortopological equivalent of a helix, whereby a broad band load isobtained.

Another feature of the present invention is the same as any one or moreof the preceding features including the provision of a dielectricstructure disposed within the delay line portion of the loss section fordisplacing some of the wave'energy attenuative liquid for reducing thedielectric loading of the loss section of transmission line.

Another feature of the present invention is the same as any one or moreof the preceding features including the provision of a transitionsection at the input end of the loss section for gradually'decreasingthe axial group velocity of wave energy traveling in the direction ofpower flow on the delayline for reducing wave reflection from the delayline.

Another feature of the present invention is the provision of an abruptimpedance matching transition at the partitioning wall between theattenuative liquid filled loss section and the transmission line inputto the loss section.

Other features and advantages of the present invention will becomeapparent upon a perusal of the following specification taken inconnection with the accompanying DRAWING wherein:

BRIEF DESCRIPTION OF THE DRAWING The DRAWING is a longitudinal sectionalview of a coaxial water load incorporating features of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the DRAWING,there is shown a coaxial water load 1 incorporating features of thepresent invention. The water load 1 includes an input section ofair-filled coaxial line 2 connected to a loss section of coaxial line 3via the intermediary of an abrupt impedance-matching transition section4 formed by a wave-permeable water-impervious dielectric disc 5, as ofteflon, sealed between the inner conductor 6 and the outer conductor 7of the input section 2 of air-filled coaxial line. The characteristicimpedance of the abrupt transition water load having reduced section 4is made substantially equal to the characteristic impedance of the50-ohm coaxial linesection 2'by undercutting the center conductor 6 at 8and by enlarging the inside diameter of the outer conductor 7 at 9 tocompensate for the increased dielectric constant of the teflon-filledtransition section 4 of the coaxial line. By an abrupt transition it ismeant that the wave-permeable partition 5 has an axial lengthsubstantially less than one-quarter wavelength at the center frequencyof the operating band of the load 1.

The loss section of coaxial line 3 includes an inner conductor 11coaxially surrounded by a'h'ollow cylindrical outer con ductor 12. Ahollow cylindrical dielectric'sleeve structure 13, as of teflon,coaxially surrounds the inner conductor 11 and is interposed in thespace between the inner conductor 11 and the outer conductor 12 forreducing the dielectric loading of the loss section of coaxial line 3.

The loss section 3 includes an input conduit 14 and an output conduit 15communicating through a conductive end closing wall 16 which closes offthe terminal end of the load 1 and provides a wave-reflectivediscontinuity at the terminal end for reflecting wave energy back intothe loss section 3 for further attenuation. A stream of wave energyattenuative liquid, as of water, is conducted through the coaxial losssection 3 in wave-energy-exchangingrelation with wave energy travelingtherein for attenuating wave energy. In the case where water is utilizedas the wave energy attenuative liquid, the dielectric constant of thewater dielectric fill is approximately 81 such that the impedance of thewater-filled loss section 3 would ordinarily be decreased byapproximately a factor of 9 as compared to a similar air-filled section.Therefore,

a the teflon sleeve 13 is provided to reduce the dielectric loading ofthe loss section of coaxial line 3 by displacing some of the waterbetween the inner and outer conductor 11 and 12, respectively. Inthis-manner, the diameter of the inner conductor 11 can be maintained ata reasonable diameter consistent with the power-handling requirements ofthe inner conductor 11 while maintaining a 50.0 characteristic impedanceto match the impedance of the transition 4 and the input line 2. Inaddition, the inner conductor 11 is preferably made of a material whichretains its strength at relatively high temperatures, such as stainlesssteel or Monel.

The loss section of coaxial line 3 also includes a delay-line section 18and a delay-line transition section 19; In the delayline section 18 theinner conductor 11 is wound into a helix to form a helical delay-line,thereby substantially reducing the group velocity for wave energytraveling on the helix in the TEM mode.

In the delay line transition section 19, the inner conductor 11 has aninitial straight portion having a length sufficiently long to extendbeyond the local electromagnetic fields of the discontinuity produced bythe abrupt transition section 4. The straight portion of the innerconductor 11 is followed, taken in the direction of power flow,indicated by the arrow p, by a helix having a conically tapered diameterd, which increases in the direction of power flow. The diameter of thehelix increases throughout the transition section 19 until it reachesthe diameter of the helix in the delay section 18. The transitionsection 19 performs two functions, first, it forms a velocitytransformation for transforming the group velocity of wave energy on thecoaxial'line from the velocity of light to a substantially slower groupvelocity in the delay line section 18, as of one-tenth the velocity oflight. Secondly, transition section 19 provides an impedance transitionsection for transforming the impedance from the 509. characteristicimpedance at the power input end of the loss section 3 to a relativelylow characteristic impedance of approximately for the helix as immersedin water in the delay-line section 18.

The wave energy attenuative liquid passes into the loss section 3 viainput conduit 14 and is passed through the annular chamber 21 betweenthe teflon sleeve '13 and the outer conductor 12 to the power input endof the loss section 3 at which point the attenuative liquid flows to thecenter of the sleeve 13 via a plurality of inclined bores 22 passingthrough the wall of the sleeve 13. The attenuative liquid within thecenter of the sleeve 13 immerses the helical delay-line and transitionsection in the wave energy attenuative liquid, thereby greatlyattenuating the wave energy on the helical portion of the centerconductor 11.

In the typical example of a coaxial water load 1, for use in the UHFband from 450 MHz. to 900 MHz., the inner conductor 11 has a diameter ofthree-sixteenths of an inch which tapers over a 6-inch length to a helixof an outside diameter of 1 inch with a pitch of five-sixteenths of aninch. The attenuation for wave energy within the delay line section 18is approximately 0.94 db. per inch. Thus, a section 5.3 inches longyields db. for wave energy traveling in one direction. The teflon sleevehas an outer diameter of 2.0 inches and an inside diameter of 1.285inches and the outer conductor 12 has an inside diameter of 3 inches.

In an alternative embodiment, not shown, the inside diameter of theteflon sleeve 13 is bored to a larger diameter in the delay line section18 since the dielectric sleeve structure 13 is not required in thisregion for impedance matching purposes. The diameter of the helix in theloss section would then be increased to the inside diameter of the boredteflon sleeve to further decrease the group velocity for wave energytraveling in the delay-line section 18. If the helix is increased to1.75 inches in diameter the axial length of the delay line section 18can be reduced to 3 inches for 5 db. of attenuation for energy travelingin one direction.

Although the helix delay-line has been shown for the inner conductor 11,it is to be understood that other types of delay lines may be employedsuch as topological equivalents of the helix or helix derived circuits,namely, crosswound helices, bifilar helices, ring and bar, and doublering and bar slowwave circuits. It is also to be understood that othertypes of periodic loading for the center conductor may be employed suchas a disc-loaded center conductor. Also, other types of delay-lines maybe employed for the center conductor such as a meander line. As analternative, the outer conductor 12 of the loss section 3 may includeperiodic loading members for decreasing the group velocity of waveenergy traveling in the loss section 3.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a load for dissipating electromagnetic energy in a transmissionline into a liquid coolant, a loss section of coaxial transmission linehaving a portion of the inner conductor thereof comprising a delay-lineportion, and means for directing a stream of wave attenuative liquidthrough said loss section of line in wave-energy-exchanging relationwith the wave energy on said delay-line for attenuating the wave energy,whereby the physical length of said loss section is reduced for a givenamount of attenuation, and further including a dielectric structureinterposed in said delay-line between said inner conductor and saidouter conductor, said dielectric structure having a dielectric constantsubstantially less than the dielectric constant of the wave-attenuativeliquid to be passed through said loss section of coaxial line forreducing the dielectric loading of the loss section of the coaxial line.

2. The apparatus of claim 1 wherein said delay-line inner conductor is ahelix or topologically equivalent helix.

3. The apparatus of claim 1 including a conductive end closing walldisposed at the terminal end of said loss section and interconnectingsaid inner delay-line and said outer conductor to provide a wavereflective termination for said loss section.

4. The apparatus of claim 1 wherein said delay-line has a portion withtapered dimensions in the direction of power flow within said losssection for gradually decreasing the axial group velocity of wave energytraveling on said inner delayline in a direction of power flow therealon5. The apparatus of claim 4 wherein said inner delay-line is a helix andwherein the tapered dimension of said helix is the diameter, suchdiameter increasing in the direction of power flow on said helix.

6. The apparatus of claim 1 wherein said dielectric structure comprisesa dielectric sleeve disposed coaxially of and surrounding saiddelay-line.

7. The apparatus of claim 1 wherein said means for directing a stream ofwave attenuative liquid through said loss section includes means forimmersing said delay-line in the stream of wave attenuative liquid.

8. The apparatus of claim 1 including a liquid-impervious dielectricwave-permeable structure sealed across said loss section of coaxial linebetween said inner conductor and said outer conductor at the wave energyinput end of said loss section for partitioning an attenuativeliquid-filled portion of said loss section from an input coaxial-linesection to be connected to the input end of said loss section.

9. The apparatus of claim 8 wherein said dielectric partitioningstructure is a disc, and including inductive reactive means disposed atsaid disc for impedance-matching said disc to said liquid-filled losssection.

10. The apparatus of claim 1 wherein said liquid-filled loss section ofcoaxial line proximate said partitioning wavepermeable structure isdimensioned to have a characteristic impedance when filled withattenuative liquid which is substantially equal to the characteristicimpedance of said coaxial line proximate the side of said partitioningwave-permeable structure opposite to said liquid-filled side to providea broadband substantially wave-reflectionless transmission linetransition to said liquid-filled loss section.

1. In a load for dissipating electromagnetic energy in a transmissionline into a liquid coolant, a loss section of coaxial transmission linehaving a portion of the inner conductor thereof comprising a delay-lineportion, and means for directing a stream of wave attenuative liquidthrough said loss section of line in wave-energy-exchanging relationwith the wave energy on said delay-line for attenuating the wave energy,whereby the physical length of said loss section is reduced for a givenamount of attenuation, and further including a dielectric structureinterposed in said delay-line between said inner conductor and saidouter conductor, said dielectric structure having a dielectric constantsubstantially less than the dielectric constant of the wave-attenuativeliquid to be passed through said loss section of coaxial line forreducing the dielectric loading of the loss section of the coaxial line.2. The apparatus of claim 1 wherein said delay-line inner conductor is ahelix or topologically equivalent helix.
 3. The apparatus of claim 1including a conductive end closing wall disposed at the terminal end ofsaid loss section and interconnecting said inner delay-line and saidouter conductor to provide a wave reflective termination for said losssection.
 4. The apparatus of claim 1 wherein said delay-line has aportion with tapered dimensions in the direction of power flow withinsaid loss section for gradually decreasing the axial group velocity ofwave energy traveling on said inner delay-line in a direction of powerflow therealong.
 5. The apparatus of claim 4 wherein said innerdelay-line is a helix and wherein the tapered dimension of said helix isthe diameter, such diameter increasing in the direction of power flow onsaid helix.
 6. The apparatus of claim 1 wherein said dielectricstructure comprises a dielectric sleeve disposed coaxially of andsurrounding said delay-line.
 7. The apparatus of claim 1 wherein saidmeans for directing a stream of wave attenuative liquid through saidloss section includes means for immersing said delay-line in the streamof wave attenuative liquid.
 8. The apparatus of claim 1 including aliquid-impervious dielectric wave-permeable structure sealed across saidloss section of coaxial line between said inner conductor and said outerconductor at the wave energy input end of said loss section forpartitioning an attenuative liquid-filled portion of said loss sectionfrom an input coaxial-line section to be connected to the input end ofsaid loss section.
 9. The apparatus of claim 8 wherein said dielectricpartitioning structure is a disc, and including inductive reactive meansdisposed at said disc for impedance-matching said disc to saidliquid-filled loss section.
 10. The apparatus of claim 1 wherein saidliquid-filled loss section of coaxial line proximate said partitioningwave-permeable structure is dimensioned to have a characteristicimpedance when filled with attenuative liquid which is substantiallyequal to the characteristic impedance of said coaxial line proximate theside of said partitioning wave-permeable structure opposite to saidliquid-filled side to provide a broadband substantiallywave-reflectionless transmission line transition to said liquid-filledloss section.